landy andy wrote:

NO AERIAL IS PRE-TUNED

That would be my first advice.

Run good quality cable, making sure inner core doesn’t touch out cores, and tune your aerial. I’ve always had to remove a few inches or more.

A well placed aerial is best, so slap in the middle of the roof is ideal. A massive great earth cable to the aerial mount is great. But I’ve never done either of these and I’ve had numerous setups, always with a great range.

I think you will be surprised once you tune it.

walfy wrote:

As said, no arial is pre tuned. It all depends on the ground plane that you have. In the centre of the mass is best which gives the best 360 deg projection of signal.
Lifted from the net, a bit heavy going but explains it correctly

Radio antenna theory

In telecommunication, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements. The plane does not necessarily have to be connected to ground. Ground plane shape and size play major roles in determining its radiation characteristics including gain.
For a monopole antenna, the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from an image antenna.

To function as a ground plane, the conducting surface must be at least a quarter of the wavelength (λ/4) of the radio waves in diameter. In lower frequency antennas, such as the mast radiators used for broadcast antennas, the Earth itself (or a body of water such as a salt marsh or ocean) is used as a ground plane. For higher frequency antennas, in the VHF or UHF range, the ground plane can be smaller, and metal disks, screens and wires are used as ground planes. At upper VHF and UHF, the metal skin of a car or aircraft can serve as a ground plane for whip antennas projecting from it. In microstrip antennas and printed monopole antennas an area of copper foil on the opposite side of a printed circuit board serves as a ground plane. The ground plane doesn't have to be a continuous surface. In the ground plane antenna style whip antenna, the "plane" consists of several wires λ/4 long radiating from the base of a quarter-wave whip antenna.

The radio waves from an antenna element that reflect off a ground plane appear to come from a mirror image of the antenna located on the other side of the ground plane. In a monopole antenna, the radiation pattern of the monopole plus the virtual "image antenna" make it appear as a two element center-fed dipole antenna. So a monopole mounted over an ideal ground plane has a radiation pattern identical to a dipole antenna. The feedline from the transmitter or receiver is connected between the bottom end of the monopole element and the ground plane. The ground plane must have good conductivity; any resistance in the ground plane is in series with the antenna, and serves to dissipate power from the transmitter.

Just to add to the super explanation above, here is an image to illustrate how positioning of an aerial and the ground plane can effect the signal strength and coverage;




And how aerials with different gain levels and topography affect your operational range.




I cannot remember where I found these, but have had them saved as reference for ages...